1. Field of the Invention
The present invention relates to a vehicle brake fluid pressure control device with a hydraulic booster to be used during normal braking control operations, in particular, applicable to an electric vehicle that does not use engine vacuum.
2. Related Art
In a conventional hydro booster or an EHB (Electro Hydraulic Brake), brake pressure to be used during normal braking is amplified by using a high capacity accumulator (e.g., refer to Japanese patent No. 2,765,570).
However, in the hydro booster or EHB, the high pressure maintained at all times with the high capacity accumulator. Therefore, it is necessary for the brake system to be equipped with a fail-safe mechanism for ensuring the high pressure so that the brake system is complicated. Further, this brake system has a drawback that nitrogen gas or the like for maintaining the high pressure may leak through a seal, resulting in that not only the high pressure may not be maintained but also the leaked nitrogen gas or the like may enter into a brake piping conduit.
Furthermore, an urgency brake control such as the ABS control, the TCS control or vehicle stability control, which are executed during a vehicle running, requires quick responsiveness to brake fluid pressure applied by a pump. In order to implement the quick responsiveness to pressure, a brake device having a brake fluid amount amplifier provided between a master cylinder and a wheel cylinder has been proposed (e.g., refer to Japanese patent publication No. 10-35459).
In this brake device, it is assumed that the pump is used only during the urgency control operations, but not during the normal braking operation. Accordingly, while a problem of the quick responsiveness to pressure still remains in view of a size or efficiency of the motor, it is very difficult to provide a system or control that can endure the highly frequent use at the normal braking operations.